Isoquinoline alkaloids (IQAs) are a large group of alkaloids and include many pharmacologically useful compounds. In the biosyntheses of IQAs, P450-mediated hydroxylation, methylenedioxy bridge-formation, and phenol coupling reactions have been reported. While members of the CYP80B subfamily catalyze hydroxylation reaction, other P450 reactions, including methylenedioxy bridge-formation and phenol coupling reactions, are involved in the biosynthesis of rather specific IQAs. Our recent research identified that all CYP719A subfamily members (CYP719A1, 2, 3, 5, 9) so far characterized catalyze methylenedioxy bridge-formation in IQA biosynthesis. On the other hand, some P450-mediated phenol coupling reactions have been also reported in IQA biosynthesis, i.e., intramolecular C-C phenol coupling (e.g., CYP80G2) and intermolecular C-O phenol coupling (e.g. CYP80A1) reactions. We discuss the role of the unique amino acid residue in these P450s in the reaction.
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